The present invention is in the field of assembly systems for articles made of limp material, and more particularly related to sewing machines.
Sewing machines are well known in the prior art to join portions of a multiple layer limp fabric (or material) workpiece along a curvilinear path, thereby forming a seam. Generally, such machines include a needle adapted for reciprocating motion along a needle axis which is angularly offset from a planar workpiece support surface. In most prior art sewing machines, manually or automatically controlled, feed devices present the fabric-to-be-joined to the needle along a feed axis which is fixedly positioned with respect to the needle axis and the workpiece support surface. By way of example, such devices include feed dogs, rolling cylinder feeds and tractor feeds (using endless belts over rollers).
Robots have long been applied successfully throughout industry in a variety of applications as diverse as welding, painting and assembly. By far the most challenging of these applications has been assembly. A significant amount of Progress has been made in improving the ability of robots to accomplish complex assembly tasks but for the most part research has concentrated on assembly of rigid parts made of hard plastic and metals, materials typically found in assembly of small mechanical or electrical devices. Much less research has been directed towards the assembly of flexible parts such as textiles. Development of flexible material handling technology is necessary in order to introduce robotics into industries based on flexible, or limp, materials, such as apparel manufacturing.
Since textiles are flexible materials, they pose problems for robotic manipulation which were not encountered in rigid parts manipulation. The inherent limpness of textiles necessitates design of specialized handling equipment to assure that the flexible workpiece does not distort during handling. This equipment must be designed to be robust to material properties which affect handling that vary not only from part to part, but also within a single part.
In recent years, there have been significant advances in the automated control of limp material segments, particularly suited for apparel manufacture. By way of example, U.S. Pat. Nos. 4,632,046, 4,607,584, 4,719,864, 4,651,659 and 4,638,749, all assigned to the assignee of the present invention, disclose systems and methods for manipulating and controlling limp material segments generally for presentation to seam joining assemblies, e.g. sewing machines. All of these patents are concerned with the fact that the limp materials are easily deformed. Since the edges of cloth panels which must eventually be aligned are easily deformed, multiple support points are required. Typically, the support points must be placed close enough to the desired edge so that distortions such as curling or folding do not occur during transport. The placement is further complicated by the fact that the cloth's tendency to curl, fold, or wrinkle is highly dependent on material properties such as bending rigidity. Bending rigidity will vary from part to part as material changes (e.g. polyester or wool) and can even vary within a single part, depending on orientation of the gripper to the weave or proximity of the gripper to reinforcements. During manipulation of flexible materials, such as textiles, little force is transmitted back t the positioning device, since the workpiece is easily distorted. As a result, non-contact sensing methods such as vision are often utilized for final alignment before establishing a seam.
U.S. Pat. No. 4,719,864 discloses a feed assembly for a sewing machine which provides near needle control of the segments-to-be-joined.
In connection with automated sewing systems, it has proved to be very difficult to get the ends of a long seam to match up when two plies are sewn together. Slight errors in differential feeding of the two plies to the needle accumulate to large errors by the end of a long seam. Other sources of errors result from uneven drag on the cloth and from mis-cut lengths of material. When the seam is sewn by hand, measures can be taken to correct any noticed misalignment. However, automatically sewn seams using prior art systems generally have large errors if no correction method is used.
Moreover, in many sewing applications, cloth panels cannot always be held firmly in place during the sewing operation since for proper alignment to occur the two cloth parts must be allowed to move in the direction parallel to the seam direction. This motion is accomplished by "ply shifting", i.e. moving one ply relative to another, during the seaming operation. In the simplest case, when two seams are joined, no ply shifting is introduced resulting in a flat seam after sewing. If one ply is shifted relative to another during sewing, then bunching occurs, This effect, known as easing, may be selectively utilized to shape garments during seaming.
In the prior art, several methods have previously been used to control end alignment and easing. The most common method is to use a human operator, together with workpieces having reference notches cut into the edges of the segments-to-be-joined, where the notches are positioned to overlap when the seam is properly established with desired easing. As the operator hand sews, he attempts to align the notches. This operation requires great skill but is tedious and characterized by relatively low productivity. Further, good operators are hard to find.
Alternatively, automatic machines without end feedback are used, where end alignment control is manually adjusted during sewing so that the ends visually line up after seaming. However, slight variations in material properties can cause end aligning errors. This problem becomes amplified with longer seams.
More recently, sewing systems have used a single "mouse" whereby both ply end corners (at the end of the desired seam-to-be-made) are clamped together prealigned. The workpiece bearing the opposite end of the seam is then drawn toward the needle while the mouse is dragged along to maintain tension and to assure the trailing ends line up. The main problem with this method is that the easing profile throughout the seam is not well controlled. Normally, if plies are miscut, it is considered best to put constant, minimal, easing all along the seam to correct for the length error. However, with the single mouse system (due to properties of feed dog mechanisms), a high amount of easing is generally established at the beginning of the seam, and the easing typically drops to zero easing by the end of the seam. In attempting to overcome this deficiency, some single mouse machines have a differential feed mechanism where an easing profile can be programmed for the entire length of the seam. The problem with this approach is that such easing is accomplished in an open loop manner and any easing caused by the mouse is uncontrolled.
Accordingly, it is an object of the present invention to provide an improved system for establishing a seam joining two (or more) limp material segments.
Another object is to provide an improved seam joining system permitting establishment of seams with continuous control of the regions of the materials being joined.
It is another object to provide an improved seam joining system in which distal ends of the materials-to-be-joined are controlled during the joining operation.
Yet another object is to provide an improved seam joining system permitting predetermined easing to be incorporated on a continuous basis during a seam joining operation.
Still another object is to provide an improved seam joining system permitting predetermined easing to be incorporated in both workpieces-to-be-joined.